First case of three-way multiple herbicide resistance in Amaranthus palmeri outside the Americas: Resistance mechanisms and alternative management strategies
The rapid spread of herbicide-resistant Amaranthus palmeri S. Watson across the Mediterranean region poses a severe threat to crop production. This study characterizes the resistance profile of an A. palmeri population from Gonen, Israel, which survived multiple post-emergence herbicide applications in maize. Greenhouse dose-response and screening trials were conducted across four modes of action…
An A. palmeri weed population in Gonen, Israel, has been found to possess three-way multiple herbicide resistance outside the Americas. This study reveals that the resistant plants exhibit resistance to acetolactate synthase (ALS), photosystem II (PSII), and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors. The high-level resistance to ALS inhibitor foramsulfuron and PSII inhibitor metribuzin was demonstrated, with 40-70% and 80-100% survival, respectively, even at double the recommended field rate. The ALS gene sequencing indicated a Trp574 to Leu substitution as the resistance mechanism.
The weed population also displayed differential sensitivity to PSII, as atrazine provided complete control despite metribuzin's high survival rate. Sequencing did not uncover any known psbA mutations, and malathion pre-treatment only slightly reduced metribuzin survival. Partial resistance to tembotrione (HPPD inhibitor) was observed, with pre-treatment reducing survival by 20-30%. Conversely, pre-emergence applications of S-metolachlor, isoxaflutole, and a fomesafen + terbutryn mixture significantly reduced emergence.
These findings confirm the emergence of multiple-resistant A. palmeri in the region, emphasizing the critical need for integrated weed management strategies incorporating effective pre-emergence herbicides instead of relying solely on post-emergence chemical control in summer cereal rotations.
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